Rotary electric machines that are closely related to industries and daily life are foundation devices that support modern society. Especially, in hybrid cars and electric cars that are becoming popular from the viewpoint of protection of the global environment, reduction in size and weight is required for motors of power sources from the viewpoint of securing of a mounting space and improvement of fuel consumption through the reduction in weight.
Stator slot insulation of a power motor for hybrid cars and electric cars is configured from a slot insulating paper inserted between a stator core and a coil and between different phase coils, and a fixing varnish filled in gaps between the stator core and the coil and between the different phase coils to fix the coil and the slot insulating paper to the stator core.
In the slot insulation, a difference in dielectric constant between the air existing between the slot insulating paper and the stator core, and the slot insulating paper is large near a slot end portion of the stator core, and thus an electric field is concentrated in an air layer near the slot end portion, and partial discharge occurs at a low voltage between the slot insulating paper and the stator core. This partial discharge erodes an insulating layer and is finally led to dielectric breakdown during operation of the motor. Therefore, occurrence of no partial discharge is an essential condition in the stator slot insulation of the power motor for hybrid cars and electric cars.
As means for reduction in size of the power motor, achievement of a high drive voltage is conceivable. To cope with the high drive voltage on an extension of a conventional technique, a technique for increasing the thickness of the slot insulating paper to secure an insulation distance corresponding to a working voltage is conceivable. For example, PTL 1 discloses a technique for adjusting a total thickness of a slot liner by multilayering the slot liner according to a shared voltage.